Electrical motor control apparatus



Feb. 17, 1948.

Egg.

H. E. HARTIG ELECTRICAL MOTOR CONTROL APPARATUS Filed Oct. 9, 1942 3 Sheets-Sheet l Feb. 17, 1948.

H. E. HARTIG 2,435,965

ELECTRICAL MOTOR CONTROL APPARATUS Filed Oct. 9, 1942 3 SheetSI-Sheet 2 I-MIIIIIMI/- /06 09 Gftorncg Feb. 17, 1948.

H. E. HARTIG ELECTRICAL MOTOR CONTROL APPARATUS Filed vOG'l.. 9, 1942 3 Sheets-Sheet 3 attorneg Petenfed Feb. 17, 194s 2,435,965 ELECTRICAL MOTOR CGNTRGL APPARATUS Henry E. Har-tig, Robblnsdale, Minn., assigner to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application October 9, 1942, Serial No. 481,403 17 Claims. (Cl. S18-29) The present invention is concerned with a motor control system and more particularly with one in which the energization oi' the motor is controlled by an electronic discharge device.

An object of the present invention vis to provide s. motor conttol system in which the motor is controlled by a gas yfilled electronic discharge device in which a direct current voltage is applied to the gaseous discharge device continuously except for very brief intervals so that when the grid voltage is such as to call for the discharge device to energize the motor, such Ienergization takes place substantially continuously.

A further object of the invention is to provide such a system in which the voltage applied to the grid is periodically increased for fixed periods of time.

A still further object of the invention is to provide such a system in which the number of periods of increased voltage applied to the grid bears a definite predetermined relation to the number of periods during which voltage is applied to the discharge device.

A further object of the present invention is to provide an arrangement in which the several increases in grid voltage applied during successive periods are of different magnitudes.

A further object of the present invention is to provide an arrangement in which the grid voltage of a grid controlled electronic discharge device is controlled by a resistance bridge and in which the voltage applied to the resistance bridge is periodically increased for periods of relatively short duration.

A still further object of the present invention is to provide an arrangement employing an electronic discharge device for controlling the energization of a current responsive element in which one means is applied for normally energizing the grid and in which a second means is applied for superimposing a further voltage upon the normal grid voltage for periods of extremely short duration.

Other objects of the invention will be apparent from a consideration of the accompanying specification, claims and drawings, of which Figure 1 is a schematic view of one form of my motor control system,

Figure 2 is a diagrammatic representation of the grid and plate voltages in such a system,

Figure 3 is a schematic view 'of a modified form of my motor control system, g

Figure 4 is a diagrammatic representation of the grid and plate voltages in connection with the system of Figure 3. and

Figure 5 is a schematic representation of a motor control system similar to that of Figure 1 with the exception that it is adapted for the control of two separate motors.

Referring to the drawing for a more detailed understanding of my invention, the motor to be controlled is indicated by the reference numeral I0. This motor may be of any various types having a pair of direct currentv paths therethrough, the direction and rate of rotation of the motor depending upon the relative amounts of current flowing through the two paths. As shown in the drawing, the motor is a direct current motor having a plurality of iield windings II and I2 connected in series vwith the armature I3 of the motor. When the current ilow through field winding II is greater than that through field winding I2, the motor rotates in one direction. When, on the other hand, the current flows through field winding I2 is greater. the motor rotates in the opposite direction. A condenser IB is connected in parallel with winding II and the armature I3. A second condenser Il is connected in parallel with winding I2 and armature Il. The relative energization of field windings II and I2 is controlled by a pair of gas filled thermionic discharge devices I4 and Il. The discharge device or tube I4 comprises an envelope having a cathode Il. a cathode heater.

Il, a control grid 20, a shield grid 2|, and an anode 22. The envelope is filled with a suitable gas. A tube which I have found particularly desirable for this purpose is the type 2050 gas illled tube. The discharge device or tube I5 is identical to discharge device Il and comprises a cathode 2|, a heater 25, a control'grid 26, a. shield grid 2l, and an anode 2l.

A potentiometer 2B, comprising a resistance II and a slider 32, is employed to control the amount of bias voltage applied to the control grids 20 and 26 The controlling voltage that is applied to the control grids 20 and 26 is obtained from a bridge circuit 33 including potentiometers 34 and Il. Potentiometer 34 constitutes the controlling potentiometer and comprises a resistance 36 and a slider 31. The slider Il is connected by a link to ,a controller 3l which may be responsive to any desired condition. The controller 35 consists ot a resistance 39 and a contact arm 40. The contact arm 40 is slidable over resistance 39. Contact arm l! is angularly positioned by a shaft II which is insulated from contact arm 40. 'Phe` shaft 4I -is positioned by motor armature I3 through a gear train 42. The output end of the gear train 42 is connected to a controlled device 43 andto shaft 4|. Thus, contact arm 48 is positioned in accordance with the position of a controlled device.

The resistors 29 and 39 are connected together v45 to the upper terminal oi' a center tapped re sistance 4l. Contact arm 48 is connected by conductor 49 to the other terminal of resistance 44, Thus the output of the bridge 33 is impressed across resistor 44. The upper terminal of resistor 44 is connected by conductors 41 and 48 to control grid 28, while the lower terminal of resistor 44 is connected by conductors 88 and 8| to the grid 28. The center tapvof resistor 44 is connected by a conductor 54, the slider 32, resistor 3|, and conductor 51 to the junction of conductors 58 and 59 connected to cathodes 8 and 24, respectively. A condenser 9i is connected between grid 28 and cathode il and a similar condenser 88 is connected between grid 28 and cathode 24. These condensers act as filtering condensers asl will be pointed out presently.

The power for operation ofthe system is obtained from a battery 68. In one proposed application of the system, the motor i8 is used to control elements connected with an airplane. In such a case, a direct current source of 28 volts is available. The battery 98 should accordingly be considered for purposes of illustration as a 28 volt battery. The battery 88 is employed to energize a combined generator and motor unit such as is commercially sold under the name of Genemctor. In such a unit, a single armature is operated in a conventional manner as an armature of a direct current motor. Through auxiliary windings associated with the armature, voltages of various magnitudes can be obtained. This is conveniently indicated in the drawing by showing a motor 18 and plurality of generators 1| and 12. While in such a motor and generator unit there is only one armature, the motor and generators are schematically illustrated for convenience .of illus tration as though they each constituted a complete unit with an armature. The motor 10 is directly connected through conductors 1,4, 15, 16 and 11 across the battery 68. The alternating current generator 1| is employed to generate an alternating current voltage of approximately 120 cycles per second. The direct current generator 12 is designed to produce a direct current voltage of approximately 230 volts. The output of alternating current generator 1| is employed to energize the bridge 33. The output terminals of generator 1| are connected through conductors 19 and 88 to a primary winding 8| of a step-up transformer 82. 'I'he transformer 92 is provided with a center tapped secondary winding 83. A grounded electrostatic shield surrounds the secondary winding 83.

The secondary winding 83 is'connected to the full wave rectifier tube 85, A tube which I have found particularly adaptable for this purpose is the 7Y4 tube. Such a tube comprises a pair of anodes 88 and 91 and a pair of filament cathodes 88 and 89. As is customary with such-full wave rectifier circuits, the cathodes 88 and 89 are connected together and to a conductor 98 leading to one input terminal of a filter network 92. A conductor 9| connected to the center point of the secondary winding Il is connected to the other input terminal of the lter network 82. The filter network 92 comprises a pair of resistances 93 and 94 in one side and a pair of resistances 95 and 98 in the other side. A condenser 91 is connected between the junctions of the two pairs of resistances and a further condenser 98 is connected across the output ends of resistors 94 and 96. The operation of the full wave rectifier tube 85 and the lter network 92 is entirely conventional and need not be described in detail here.' Upon the transformer 82 being energized, the tube 85 acts to impressacross input terminals of the filter net work a full wave rectified voltage. This voltage in passing through the filter network is smoothed out so that the voltage across the output terminals consists of a substantially constant direct current voltage. The output terminals ot resistors 94 and 98 are connected by conductors 99 and |88 to the opposite ends of resistor 36 and hence serve to impress across the input terminals of the resistance bridge 33 the direct current voltage supplied by the action of transformer 82, rectifier tube 85, and the filter network 92, A pair oi.' condensers |8| and |82 are connected between the Junctions of resistors 93 and 94 and resisters and 99 and ground. Condensers |8| and |82 serve to by-pass any disturbances that might exist between the conducting network and ground.

The direct current generator 12 is employed to supply power to the output circuits of discharge devices i4 and l5 and hence to energize the motor I8. A filter condenser |85 is connected by conductors |88 and |81 directly across the' output terminals of generator 12, The condenser |85 functions to filter out any small ripples that may exist in the output of generator 12. A resistor |89 is connected in series with conductor |88 and serves as a buffer between armature 12 and shortoircuitng contactar |38 to limit the current. Re-

sistor |89 is in turn connected by conductor ||8 to a terminal which will hereafter be referred to as the positive terminal of the power supply for the output circuits of discharge devices i4 and of the system will be traced from terminals and ||3 rather than from the generator 12.

The conductor |81, connected to terminal 3 by conductor ||2, is also connected by conductors ||8 and 16 to the positive side of the battery 68. 'I'he junction of conductors |81 and il! is connected to ground at ||1. Thus, the terminal ||3 is at ground potential which potential corresponds to the positive potential of the battery 68 and the negative potential of generator 12.

The resistor 3| of potentiometer 38, previously referred to, is connected by conductors 51, I8 and 9 to terminal ||3 which, as previously indicated, is connected by conductors ||2, |01, H4, and 16 to the positive terminal of battery 68. The other end of resistor 3| -is connected by conductor |28, protective resistor |2| and conductors 122 and 15 to the negative terminal of battery 68, It will accordingly be seen that resistor 3| is connected across the terminals of battery 88 so that the voltage existing across battery 68 is applied across resistor 3|. The right-hand end of re'- sistor 3| tends `to be positive and the left-hand end negative. As previously explained, the righthand end (the positive end) is connected to cathodes I8 and 28. The slider 32 is connected throughconductor 84 to the center tap of resistor 44 and through this resistor to the two con. trol grids 23 and 23. The Potentiometer 33 thus serves to apply a portion of the voltage existing between the control grids and the cathodes I and I3 in such a manner as to -bias these grids negatively with respect to the cathodes.

My motor control system employs means to periodically remove the voltage from the plate circuit and means to increase the magnitude of the grid voltage. These means will now be described.

A direct current motor is indicated by the rei erence numeral |25. One terminal of this motor is connected by conductors |25, |22 and 15 to the negative terminal of the battery. The other terminal is connected by conductors |21 and 13 to the positive terminal oi' the battery. Motor |25 is employed to drive rotary contactors |30 and |3I. The rotary contactor |30 consists ofa drum including conductive bars |32 and |33 separated by insulating material. Associated with the drum are a pair of brushes |34 and |35. The brushes |34 and |35 are so arranged with respect to the conductive bar |32 that during a very small portion of each half revolution of the rotor, a conductive circuit is established between brushes |34 and |35 through conductive member |32. At all other times, the brushes |34 and |35 are insulated from each other either by reason of one of the brushes engaging an insulating segment or by reason of the brush |34 engaging one of the conductive members and brush I 35 the other.

The brush |34 is connected by conductor |31 to Atleti'iode I4 and terminal II3. Brush |35, on the other hand, is

connected by conductors |33 and |33 to terminal ||I. It will thusbe seen that the contactor |30 serves to periodically establish a conductive path between terminals III and II3. .A resistor |40 and a condenser I4I are connected by conductors |42, |43 and |38 between brushes |34 and |35. The resistor and condenser are employed to provide a low impedance shunt for high frequency voltages across brushes |34 and |35 and hence to minimize any tendency towards sparking between brushes |34 and |35 and the conductive member |32.

The rotary contactor I3| is similar in con'struction to the contactor |30. Contacter |3| thus comprises a rotor having conductive bars |44 and |45 separated by insulating material. Cooperating .with the rotor are brushes |45 and I 41. Aa with contactor |30, the brushes |45 and |41 are electrically connected by a conductive segment I 44 4fora very brief interval during each half revolution oi the rotor. A condenser |50 is connected in series with brushes |45 and |41. Connected in parallel with condenser |50 is a resistor |5| which has a relatively high resistance value although capable of discharging condenser |50 within a relatively short period of time.

'I'he motor |25 is connected by a shaft |52 directly to the rotor of contactor |30. The motor |25, however, is connected to the rotor of contactor |3| through a reduction gear train |53, which gear train provides a reduction in speed of four to one. Hence, contactor I3| is rotated only one-fourth as fast as contactor |30 so once every four times that a circuit is established between brushes |34 and |35, a circuit is established between brushes |45 and |41.

Operation As previously indicated, the terminals I II and |I3 constitute the terminalsof a direct current voltage supply for the output circuits oi' triodes Il and I5. Thus, a circuit may be traced through ileld winding I2 as follows: from positive terminal through conductors |55 and |53. armature I3, eld winding I2, conductor |51,

anode 22, cathode I3, and conductors 53, II3 and I3 tothe negative terminal I I3. Similarly, a circuit may be traced from terminal III through conductors |55 and |53, armature I3, ileld winding II, conductor |53, anode 23, cathode 24, and conductors 53. ||3 and II3 to the negative terminal I I3. Ii it were not for the contactor |30, these connections would serve to impress across the anodes and cathodes of tubes I4 and I5 a continuous direct current voltage. In view of the fact, however, that a gaseous discharge device of the type of devices I4 and |5 will continue to conduct a current once the grid potential has risen suillciently to initiate a'conductive discharge, it is necessary to periodically remove the voltage from the anode circuit in order to determine whether -the grid voltage is still such as to call for a conductive discharge. 'I'he contactor |30 serves this purpose. It will be obvious that each time brushes |34 and I 35 are conductively connected, a direct conductive connection is established between terminals ||I and II3, which conductive connection establishes a shunt across the motor I0 and the discharge devices I4 and I5. As previously noted, condenser I5 is connected in parallel with winding |I and armature I3, and condenser |1 in parallel with winding I2 and armature I3. Thus when an energizing circuit is established through winding II, condenser I5 becomes charged and when an energizing circuit is established through winding I2, condenser I1 becomes charged. In either case, the lower terminal will be the positive terminal. When temilnals I I I and I 3 are electrically connected by contactor ||3, the condenser is effective momentarily to apply to the associated tube plate electrode a voltage opposite in polarity to that applied by the power source. Thus, considering the case in which the tube I5 is conductive so that current ilows through winding IIand condenser I5 is charged, the following circuit is established when contactor |30 connects terminals and |I3; from the lower positive terminal of condenser I5 through conductors |55, |39, and |33, brush |35. conductive bar |32, brush |34, conductors |31, I Il, I I5 and 58 to cathode 24, anode 23, and conductor |53 to the -other terminal of condenser I5. The establishment of this circuit tends to apply across the anode and cathode of tube I5 a voltage of such polarity that the cathode 24 is positive and the an'ode 23 negative. In other words, this voltage is of the opposite polarity to that normally applied by the generator 12. This effect is of very brief duration due to the fact that the condenser I5 rapidly discharges through winding I I and armature I3. However, this temporary voltage in the opposite direction exists suillciently long to insure the termination oiv any discharge through tube I 5.

It will be obvious that the same condition occurs when a tube I4 is conductive and a circuit exists through tube I4 and Winding I2. In this case, the condenser I1 is the one which is charged and upon terminals III and |I3 being connected by the contactor |30, a circuit is established as follows: fromthe lower positive termlnal of condenser I1 through conductors |55, |55, |33, and |38, brush |35, conductive bar |32. brush |34, conductors |31, II9, IIB, and 55, cathode I3. anode 22, and conductor I 51 to the other terminal of condenser I1. Theestablishment ot this circuit tends to impress a positive voltage on the cathode I8 in the same manneras was done in connection with tube I6, Again, this effect is of very brief duration due to the discharge of condenser I1 through winding I2' and armature Il. Thus the potential of either anode 22 or anode 28 is that indicated by the line |60 of Figure 2 where line |6| indicatesthe cathode potential.

It is desirable if the tubes are to be operated eiliciently that the periods in which the potential is removed from the anode circuit be relatively short. In one embodiment of my inven' tion, it was found desirable to apply a voltage to the anode for approximately 1,60 of a second and to reverse the voltage for l/w of a second. Thus, the intervals during which the voltage was applied were about ten times the length ofthe intervals during which the voltage was reversed.

As previously explained, the output voltage of the bridge 33 is applied to resistor 44. Also, as previously explained, the potentiometer 36 applies a voltage between the grids and cathodes which biases the grids negatively with respect to the cathodes by an amount dependent upon the setting of slider 32. Connected in series with this biasing voltageis a voltage existing across onehalf of the resistor 44. When the bridge 33 is completely balanced, as is shown, no voltage exists across resistor 44. Consequently, the grids and 26 are biasedl negatively to a substantial degree, as determined by the setting of slider 32.

'I'he contactar |3| is effective periodically to remove a greater portion of the biasing potential from the grids and hence to raise the potential of these grids. Whenever the position of the rotor of contactor i3! is such that brushes |46 and |41 are conductively connected, the resistor -3| is shorted out by the following circuit: from the right-hand end of resistor 3| through conductors 51, ||8 and I63,.brush |41, conductive bar |44, brush |46, conductor |64, condenser |50, and conductors |65 and |20 tothe lefthand end of resistor 3|. The .condenser IBB is of such capacity as to constitute an eiective short circuit across resistor 3| momentarily after brushes |46 and |41 are conductively connected. Thus, during this time 'which need be only as great as the ignition time of the gaseous triode. a matter of several micro-seconds, there is substantially no potential existing across resistor 3| so that the slider 32 is at nearly the saine potential as cathodes I8 and 24. In other Words, the voltage biasing the grids negatively with respect to the cathodes is removed so as to raise the grid voltage sharply to substantially that of the cathode, disregarding any voltage that might exist because of the unbalance of the bridge. As soon as condenser |50 is charged, the voltage of battery 6B less a small drop due to |5| is again impressed across resistance 3|, and when the brushes |46 and |41 are electrically separated, the biasing voltage is restored completely to its original value. Before brushes |46 and |41 are again connected during the next following cycle of operations, any charge on condenser |50 has leaked off through resistor I5| so that the condenser |50 is again capable of establishing a momentary low impedance path. The re'v sistor |2| previously referred to limits the current iiowing from the battery 68 to condenser |50 when the brushes |46 and |41 are first connected by bar |44 and thus increases the timeconstant of the short-circuiting device. In

-the cathode potential by the line' |6Ia.

other words, the resistor 2| functions to increase the time that resistor 3| is effectively short oircuited, in all, however, a matter of microseconds.

Referring to Figure 2, the instantaneous potential of the grid with respect to the cathode is indicated by the line |68. The critical grid firing potential ls indicated by the line |6| and The peaks in the grid voltage have been designated by the reference numeral |69. 'I'he condition at the extreme left-hand end of Figure 2 is that which exists when the bridge 31|V is substantially balanced, as shown in the drawing. At this time, the level of the main portion of line |88 is determined solely by the adjustment of slider 32 with respect to resistor |3I. In other words, the average potential of grids 20 and 26 with respect to the cathode is that due to the biasing means. Underthese conditions, the peak |69 does not rise quite to the critical grid ring potential that is to line |6| so that the tubes |4 and I5 remain non-conductive.

Let`it be assumed now that the condition to which the controller responds is such as to cause the slider 31 to move to the right. When this happens, the potential of tap 31 becomes negative with respect to slider d0. This causes a voltage to be impressed across resistor 44, the polarity of which is such that the lower end of resistor d@ is positive with respect to the upper end. As a result, the lower end of resistor 44 is positive with respect to the center ta-p while the upper end of resistor 44 is negative with respect to the center tap. Since the grid 26 is connected to the vupper end of resistor 44, the effect of this upper end being made more negative with respect to the center tap is to lower the potential of grid 26 still more with respect to cathode 24 so as to preclude a conductive discharge through the tube. Since the grid 20 is connected to the lower end of resistor 44, the

raising of the potential of the lower end withrespect to the center tap increases the' potential of grid 2U with respect to the cathode I8. In other words, the eiect produced is that indicated in the intermediate portion of Figure 2. It will be observed that the grid potential is still not suillcient to cause a conductive discharge through tube I4 under normal conditions of the grid voltage. When, however, the contactor |3| is effective momentarily to establish the short circuit condition across the resistor 3| to raise the grid voltage, as previously explained, the grid potential is raised to a suiciently high value as to cause the tube I4 to discharge. Since such a gas iilled discharge device remains conductive after it has once broken down, as long as voltage is applied thereto, the tube will remain conductive until the contacter IBD reverses the voltage on the anode circuit. Hence, the tube will pass current during the remaining portion of the period after the peak grid voltage is applied as indicated by the shading applied to the rst cycle of the intermediate portion of Figure 2.v Since theamount of unbalance of the bridge is suicently low that the grid potential is normally not above the cut-off point, the tube will remain non-conductive during the next three cycles. Thus, the tube ifi will be conductive only one fourth of the total time.

When the tube le is rendered conductive in the manner described, current iiows over the anode circuit or tube |`l previously traced, this circuit extending from terminal |i| through the amature I3, neld winding I 2 and the anode and cathode oi' tube I 4 back to the terminal I I3. The eii'ect of the flow of this current is to energize field winding I2 and amature I3 in such a manner as to cause rotation of the amature I3 in a predetermined direction. The rotation of this armature in turn causes the controlled device 43 to be shifted in position. Also, the contact arm It is moved to the right so as to tend to assume e position corresponding to the position of contact 3l and so as to rebalance the bridge 33.

Under normal conditions. the bridge will be rebaianced so that no 'voltage will be impressed across resistor Il and so that the voltage impressed on the grids 25 and 28 will again assume the value indicated in the extreme left-.hand portion of Figure 2. Under the conditions just described, in which the tube III is energized only one-quarter of the time. the motor adjusts the control device 43 and the contact arm 40 very slowly. This is advantageousin that it prevents overshooting oi the control system with resultant hunting.

Let it be assumed that the condition to which the controller is responsive is changing sutilciently fast that the slider 31 is moved further to the right than in the case just considered. Under these conditions, the amount of unbalance may be shifted sumciently so that the grid volt'- age assumes the condition shown in the Aextreme right-hand portion of Figure 2. When this happens, the potential of the grid 2li is at all times above the cut-oil? potential so that the tube il will be conductive durine,r every cycle. In other words. the tube Il will be continuously conductive except during the brief intervals in which the contactor I 30 is operating to establish a circuit between terminals I I I and I I3. Under these conditions, the motor I II will move continuously to rebalance the bridge. This continuous movement will occur until the bridge is suiliciently rebalanced as to result in the condition shown in the center portion of Figure 2. As soon as the bridge is rebalanced to this extent. the action previously described will result so that the motor will then be operated only one-fourth oi' the time and its movement will be considerably slower. It is thus assured that the motor. under all conditions. will rebalance the system without overshooting. This is possible because of the initial y sufiicient'ly great as to cause'the bridge 33 to be rapid movement of the motor with a subsequent slow movement as the bridge approaches balance.

In the discussion so far, it has been assumed that the slider 31 has been moved to the right of contact arm Ill. Now let it be assumed that the condition changes in such a manner that the slider 3l moves to the left.- 'I'he slider 31 will now assume a value'whiclr is positive with respect to that of contact arm lII. Under these conditions, the upper end of resistor M will be positive and the lower end negative. This results in the potential of grid 20 assuming an even more negative value while the potential of grid 28 is raised with respect to that of the cathode. In other words, the condition indicated in the center portion of Figure 2 now exists in connection with the tube I5. As a result, the tube I5 is conductive one-fourth of the time. Each time that the tube-is conductive, current flows over the anode circuit for tube I5 previously traced, which anode circuit includes the armature I3 and the field winding II. The eilect of the energization of iield winding II is to cause the substantially unbalanced. the condition indicated in the extreme right-hand end of Figure 2 may exist. In other words, the grid potential may be raised suiilciently high as to cause the tube I5 to remain conductive during every cycle.

Under these conditions, the rebalancing action of the motor will be initially more rapid and then slower, as described previously.

It will be seen from the foregoing description that my improved control system causes a con-- trol device to be very accurately positioned in accordance with the value of a controlling condition. Any tendency towards overshooting or hunting is avoided by causing the position of the motor to operate only a portion of the time when the unbalance is slight and substantially continuously when the imbalance is great. It will furthermore be seen that, unlike certain systems employing gas illled tubes, the tubes are caused to discharge almost continuously when there is need for continuous operation of the motor. This is due to the fact that the voltage is applied continuously to the plate circuits except for extremely brief intervals.

Species of Figures 3 and 4 these elements with identical reference numerals are the same, it is believed unnecessary to repeat their description in connection with Figures 3 and 4. The motor I0; the controlling bridge consisting of potentiometers. 34 and 35; the means for rebalancing the bridge by the motor; the portion of the power supply means from transformer 82 to the bridgeiand the Genemotor including motor unit ll, the generator unit I2 and the cycler i3d are all similar to those of Figures 1 and 2 and bear identical reference numerals. The distinguishing features of Figures 3 and 4 will now be described.

The Genemotor" in the species of Figures 3 not only comprises the direct current motor 1li energized by the battery 3l and the direct current generator 'I2 but it also comprises an alternating current generator III which generates a voltage of relatively high frequency as compared with that generated by generator 1I of Figure 1. Furthermore, the rotary contacter |30 is secured to the Genemotor shaft and v is driven thereby. Thus, the need for a separate motor such as motor |25. for driving the rotary contactor is eliminated.

The contactor |33 operates in the same manner as in the preceding case to establish periodically al short circuit between the terminals III B9 which in turn are connected to cathodes i8 and 24. The battery 23| hence operates to apply a predetermined negative bias to the grids -2|! and 28. If desired, means for obtaining a bias from the battery 6e may be employed in this species. In other words, a potentiometer corresponding to potentiometer 3| may be connected across battery 68 and a variable portion of the voltage eX- isting across this potentiometer may be applied to the grid circuit.

The alternating current generating unit' lli,

as previously indicated, generates a relatively high frequency current. This generating unit is connected in a circuit with the primary 8i ci transformer 82 as follows: from the lower ter minal of generator unit ill through conductor IBB, primary winding 8|, conductor |82, resistor |83. and conductor |784. The resistor 83 has associated therewith a plurality of. sliders |85, it@ and |81. These sliders are associated with rotary contactors 880, iti, and |92. All three rotary contactors are driven by a shaft iSd from the "Genemotor through a reduction gear train |95. The reduction gear train is so designed that for each four rotations of contactor |36, the shaft |95 is rotated once. In other words, the contactors |90, IEi and |82 are driven only one-fourth as fast as the contacter 30. Rotary contactor |90 consists ci a rotor having a pair of arcuate conductive members 2cd and 20| separated from each other by insulating material. Associated with the arcuate members 200 and 20| are a pair o! brushes 203 and 364. The brushes 203 and 26d are so arranged with respect to the conductive member 200 that twice during each rotation of motor I Bil, the brushes 293 and 204 are electrically connected by the conductive member will The rotary contactor Si similarly comprises a rotor having a pair of condu'ctive members 2b@ and 201 separated from each/other by insulating material. Cooperating with this rotor are a pair of brushes 208 and 20S. These brushes are likewise arranged so that twice during each rotation of the rotor of contactor tdi, the brushes are electrically connected by the conductive mennber 20S.l

Similarly, the contactar E92 comprises a blu-l rality of arcuate conductive members 2 i@ and 2li and a pair of brushes 2i2 and ZEE which in two positions of the rotation of the rotor are electrie cally bridged by the segment 2id.

The three contactors itt, le! and |92 are so arranged that the angular position at which the `respective brushes of each contactor are bridged is different for each of the contactors. In other words', as' the contactors 92, |9| and |90 rotate in ajcloclrwise direction as indicated by the arrow adjacent contactor |90, the brushes of the contactor ISIl'are rst connected, then the brushes of contactor |9|and ilnally the brushes of con tactor |92.

The three lower brushes 20|, 20B and 2|3 are all connected to the lower terminal of resistor |82 by conductors 2li, 2|8 and 2il. The upper brush 203 is connected by conductor :it to tap |85. The upper brush 208 is connected by conductor 2|8 to tap |88. The brush 2|2 is connected by conductor 220 to tap |81. Thus. as the contactors |90, ISI and |82 are rotated in a clockwise direction, various portions of resistor |83 are shorted out. At rst, the entire portion of resistor |83 from the lower terminal to tap |85 will be shorted out. Then the portion from the lower terminal to tap |83 will be shorted out. Finally, the portion between the lower terminal and tap |81 will be shorted out. The segments are so spaced that the action so far described takes place over three-eighths of a complete revolution. During the remaining one-eighth of a half revolution, no portion of the resistor i is short circuited.

Since resistor w8 is in the circuit to primary 8i, it acts to reduce the potential impressed upon primary di and hence to reduce the voltage across secondary 33.' This, in turn. reduces the voltage applied to the bridge t3. As various portions of the resistor 83 are short circuited, the potential impressed across primary Si and hence across the bridge 38 is increased. Since such short circuiting action takes place only for a very brief moment, the increase in voltage applied to the bridge will likewise be very short in duration. en the voltage across the bridge 33 is thus momentarily increased, the output voltageresulting from any unbalance of the bridge 3S will be abruptly increased so as to increase the potential applied to the grid by the bridge.

The variation of the grid voltage in the species just described is illustrated in Figure 4. In this figure, the potential oi the grid with respect to the cathode is indicated by the line 268.' The successive peaks are indicated by the characters 289, 2lb, and Eli for the first tour cycles of anode voltage, by the characters 212, 213 and 216 for the intermediate four cycles, and by the reference characters 2lb and 216 in the last group of cycles shown. When there is no unbalance at all, the grid voltage remains at the value de termined by the biasing battery 23H. Since the bridge is balanced, any increase in voltage applied to this bridge does not in any way afect the potential o' grids 2d and 2%. Ii, however, the bridge is slightly unbalanced, the effect of cyclers itil, itil and it@ is to increase periodically the unbalance voltage so as to result in peaks similar to peaks 289. 21d and 2li. In the case shown in the extreme left-hand end of Figure d, the amount of unbalance is such that when the entire portion ci the resistance from the lower terminal to tap it is short circnited, the grid potential is increased as indicated by the peak dts. The result of this is that the particular tube in question is rendered conductive during the cycle in which this peak occurs. Under the conditions shown in Figure 4, the peak 2lb. produced when a short circuit condition is established between the lower terminal of resistor i933 and tap idd, is not sufcient in magnitude toincrease the grid potential above the critical grid potential indicated by line dia. IThus, during this cvcle there is no discharge ci either tube. During7 the next cycle, only the nortion of resistor idd between the lower terminal and tan i8? is shorted out. 'This results in the peak 2W. During the next cycle. the iull resistor idd is connected in series with the primary di so that there is no increase in the grid poten-z tial at all. The result is that both tubes remain non-conductive during the last three of 7f3 the four cycles. This entire sequence is repeated assumes 13 every four cycles. Thus. as long as bridge unbalance remains the same, the motor is energized one-fourth of the time.

In the middle portion of Figure 4, the condition when the amount of grid voltage is increased, is illustrated. The amount of unbalance hasbecn shown as increased to the point where the rst two peaks 212 and 213 are oi sufficient magnitude to increase the grid potential i,

above the cut-oil' value so as to cause the tube whose grid potential is increased to become conductive. These two peaks are those occurring when taps |85 and |86 are connected to the lower terminal of resistor |83. The peak 214 which occurs when tap |81 is connected to the lower terminal is of insuiilcient magnitude to cause the discharge device in question to discharge. Consequently, under the conditions just considered, the tube is conductive only over two cycles of each four. Under the condition shown in the extreme right-hand end of Figure 4, the peaks 215, 216 and 211 are all of suiilcient magnitude to render the discharge device conductive. When however, the full resistor |83 is connected in the circuit the grid voltage is not sumcient to cause the discharge device to be conductive and consequently during the last cycle, the tube is non-conductive. Under these conditions, a discharge occurs through three-quarters of the time. In the extreme case (not shown) when the bridge is very greatly unbalanced, the voltage resulting from this unbalance even when the entire resistor |83 is connected in series with the primary |8| is suiilcient to cause the tube whose grid voltage is increased as a result oi the unbalance to be continuously conductive. Under such cases, the motor |D is continuously energized to rebalance the system.

In the foregoing description, no reference has been made to the particular circuits established through tubes Il and I5. It is to be understood 'that the operation in this connection is identically the-same as in Figures 1 and 2. In other words, when the contacter 31 assumes a position to the right ci.' the contact arm l0, the voltage of grid 20 `of tube I4 is increased so as to tend to render this tube conductive. When on the other hand. the slider 31 is to the left of contact arm |10, the potential of grid 28 is raised with respect to that of cathode 2l so as to tend to render tube I5 more conductive. In each case. the motor I0 is driven in such a direction as to rebalance the bridge 3S and to move the control device d3 in a direction to correct for the change of condition originally producing the unbalance. It will be obvious from the description so far that the motor I0 is driven either continuousiv, three-fourths of the time, one-fourth oi the time. or not at all depending upon the extent of the bridge unbalance. In this way. the position of the control device is verv quickly adjusted without any tendency towards cvershooting.

In tbe system just described, the increase in grid voltage is obtained by an increase in the voltage applied to the bridge. This has the disadvantage that the peaks vary in magnitude with the extent of unbalance. In most cases, it is more desirable to have superimposed on the normal grid voltage, peaks of constant value such as was done in the species of Figure l. The periodic increase in the voltage applied to the bridge 33 does, however. have the advantage of increasing the sensitivity of the bridge without increasing the heating of the resistors associated therewith. During the very brief period that the high voltage is applied, the sensitivity of the bridge is increased very materially. This period of application of the high voltage is insuiiiclent. however, to appreclably affect the resistors 38 and 33. This advantage is particularly important where in lieu of a potentiometer for the controlling resistance. a temperature sensitive resistor is employed. In such cases, it is very desirable to have as little heating of the resistance bridge as possible.

While I have shown the provision of peaks of varying magnitudes only in connection with the operation of Figures 3 and 4, it is to be understood that this same expedient could be employed in connection with Figures 1- and 2. In such case. a plurality of cyclers such as cyclers |30, |9| and |92 would be substituted for the single cycler |3| and connections would be made to various points of resistor |2 Species of Figure 5 The species of Figure 5 is very similar to that Oi Figures l and 2 with the exception that instead of merely providing for the control of one motor, provision is made for the separate control cf two motors, the power supply and the various contacting mechanisms being the same. For convenience in understanding the drawing, the elements which serve in connection with both motor control systems are given the identical reference numerals by which they are identified in Figure 1. Those elements of which it is necessary to provide one in connection with each of the two motors are given the same reference numerals as in Figure l followed by the suiiix letters a and b. Thus, there are two motors |0a and |0b. All of the control mechanism employed solely for the control of motor |0a is videntiied by reference numerals having the suilix letter a.

`All of the control mechanism employed solely for the control of motor |Ub is identified by reference numerals having the suillx b.

The battery 68, as with the arrangement of Figure 1, is employed to drive a motor 10 of a Genemotorn having an alternating current generating unit 1| and a direct current generating unit 12. The battery 68 also energizes a direct current motor |25 driving the contactors |30 and |3|. The direct current generating unit 12 impresses a. voltage across terminals ||i and ||3 which is applied to the plate circuits of tubes Ha, la, IIb, and |517. vAs described in connection with Figure 1, the contactor |30 operates periodically to short circuit this voltage at short intervals of time and permit the condensers |611, |1a, |611, and |1b to apply reverse voltages to the plate circuits. The potentiometer 3|a is connected across battery 68- and is employed to apply a bias'to grids Maand 26a. Similarly, the potentlometer 3|b is connected across battery E3 and is employed to apply a bias to grids 20h and 2Gb. The contacter |3| serves to periodically short circuit the potentiometers 3|a and 3|b so as tc increase substantially the potential applied to'grids 20a and 26avand also to grids 20h and 26h.

The output voltage of bridge 33a is applied across resistor-44a to raise and lower the potentials applied to grids 20a and 26a. Similarly, the output potential of bridge 33h is applied across resistor b to aiect the potential applied to grids 20h and 2Gb.

The operation of each of the motor control systems is identical to that of Figure 1. In each case, a direct current voltage is applied from the power common source to the two sets of gas filled tubes. The grids are normally subjected to a potential which is due to the combined eil'ect oi' the biasing potentiometer and to the unbalance voltage across the bridge. Once each four cycles of anode voltage, the biasing potential is removed for a short period of time to increase suddenly the grid voltage. If, when this is done the unbalance is only slight, this increase in the grid voltage causes one or the other of the tubes to discharge depending upon the direction of unbalance of the bridge. When this unbalance is only slight, the discharge will only occur during the cycle in which the grid voltage is peaked. When the unbalance is great, however, the un# balance potential in itself is sufficient to overcome the biasing potential so that the tube remains conductive for the entire time except for the brief intervals during which the plate voltage is removed therefrom.

It will be seen that with the arrangement of Figure 5, it is possible to employ the same source of power, the same contacting mechanism. and the same generators for controlling both motors. Due to the careful shielding and filtering, the operation of the one control system does not affeet the operation of the other despite the extreme sensitivity of the gas lled electronic discharge devices. The ability to use the ysame source of power, the same generators, and the same contacting mechanism becomes very important in connection with applications requiring the independent control of three or four motors in a location where space or weight is limited. A typical application in which this problem is present is that of controlling various elements in an airplane. Such a system as l have shown is admirably adapted for this application because of the extreme speed of response and because of the possibility of employing one generating and contacting equipment for all of the motor control systems. It is the latter equipment which tends to be heavier. Thus, the ability in an airplane to use this equipment for a number of motor control systems is highly advantageous.

Conclusion It will be seen that I have provided a new and novel motor control system which is extremely sensitive and which permits rapid positioning of the motor with no danger of overshooting.

While I have shown certain specic embodi ments of my invention for purposes of illustration, it is to be understood that the'invention is to be limited only by the scope of the appended claims.

I claim as my invention:

l. In motor controlling apparatus for motor means having a pair of current paths associated therewith and operable to rotate in one direction or the other depending upon Whether the current flow throughone of said paths is greater or less than that through the other, a pair of electronic discharge devices'each having a control element lfor controlling the discharge thereof, each of said devices being adapted to control the current flow through a diierent one of said two current paths, means for applying variable control voltages to the control elements of said discharge devices, and means for increasing the effect of control voltages of small magnitude, said last named means including means for periodically increasing the magnitude of the voltage applied to said control elements for a relatively brief interval of time.

2. In motor controlling apparatus for motor means having a pair oi.' current paths associated therewith and operable to rotate in one direction or the other depending upon whether the current ilow through one of said paths is greater or less than that through the other, a pair of gas lled electronic discharge devices each having a control element for controlling the discharge thereof, each or said devices adapted to control the cur rent flow through a diderent one of said two current paths, means for applying a direct current voltage to the output circuits of said discharge devices continuously except for periodic intervals of time of relatively short length, means for ap plying a voltage of the opposite polarity to said output circuits during said intervals of time, and means for applying a variable control voltage to the control elements of said discharge devices.

3. In motor controlling apparatus for motor means having a pair of current paths associated therewith and operable to rotate in one direction or the other depending upon whether the current flow through one of said paths is greater or less than that through the other, a pair of gas filled electronic discharge devices each having an output circuit and a control element for controlling the discharge thereof through said output circuit, each of said devices' being adapted to control the current flow through a difierent one of said two current paths, means in said output circuits for applying a direct current voltage to said output circuit continuously except for perlodic intervals of time of relatively short length, means for applying variable control voltages to the control elements of said discharge devices, and means for periodically increasing the magnitude of the voltages applied to said control elements for a relatively brief interval of time,

a. In motor controlling apparatus for motor means having a pair of current paths associated therewith, and operable to rotate in one direction or the other depending upon whether the current ow through one of said paths is greater or less than that through the other, a pair of gas filled electronic discharge devices each having an output circuit and a control element for controlling the discharge thereof through said output circuit, each of said devices being adapted to control the current flow through a dierent one of said two current paths, means in said output circuits for applying a direct current voltage to said output circuits continuously except for periodic intervals of time of relatively short length, means for applying variable control voltages to the control elements ai said discharge devices, and means for periodically increasing the magnitude of the voltages applied to said control elements for a relatively brief interval of time.

5. In combination, current responsive means, an impedance bridge having input terminals and output terminals, means for controlling the energization of said current responsive means in accordance with the voltage across said output terminals, means for continuously applying a voltage to the input terminals, and means for periodically increasing the voltage applied by said last named means for intervals the duration of which is a small fraction of the duration of the intervening periods of normal voltage, the magnitude of the voltage increase being dierent dur., ing successive intervals.

6. In motor controlling apparatus for controlling a plurality oi motors, a plurality of electronic discharge devices, each having an input circuit aan rent voltage to the output circuits, means for periodically and simultaneously interrupting .the application of said voltage to all oi said output circuits, a plurality oi main controllers, one for each of saidl motors, and means associated with each of said main controllers and energized by said source of power i'or applying a-voltage to the input circuit oi said discharge device to vary the energization oi' the associated motor in accordance with the condition oi the main controller, the magnitude of said voltage being dependent upon the condition of the maincontroller'.

7, In motor controlling apparatus for controlling a plurality of motors, a plurality of electronic discharge amplifiers each having an input circuit and an output circuit adapted to control the operation of a motor, a single source'otpower, means including said source of power for applying a voltage to the output circuits oi' said amplifiers, a plurality of main controllers, one for each of said motors, means associated'with each of said main controllers and energized by said source oi power for applying a voltage to the input circuit ot said discharge device, the magnitude ot said voltage being dependent upon the condition of said main controller so that the associated motor is energized in accordance with the condition of said main controller, and means energized by said source of power for periodically superimposf ing on said control voltage a direct current volt- 8. In combination, an electronic discharge ampliner having an input circuit and an output circuit, a primary source oi voltage, a motor energized by said source, means operated by said` motor for generating a. voltage of the proper characteristics for the output circuit of 'said amplifier, means for applying said voltage to said output circuit for time intervals of predetermined length, means including a condition responsive` controller for applying to the input circuit of said amplifier a control voltage whose magnitude is dependent upon `the value of the condition to which' said controller responds, and means including a contacter driven by said motorfor periodically changing the value oi' said control voltage for intervals relatively small in length compared to the intervals during which said voltage is applied to said output circuit.

9. In combination, an electronic discharge axnpliiler having an input circuit and an output circuit, a primary source oi voltage, 9, motor energi'zed by said source, means includingfa condition responsive controller for applying to the input circuit oi' said amplifier a control voltage whose magnitude is dependent upon the value oi the condition to which said controller responds, said last named means including resistance means and means including a contacter driven by said motor for periodically shunting variable portions of said resistance means to change the value of said control voltage.

Y 10. In a motor control system, a motor means, a device positioned thereby, means for energizing at least a portion of said motor means for varying portions of predetermined periods of time to vary the total movement of said device by said motor'means occurring during each of said periods of time, said controlling means including a las illled electronic discharge ampllner having an i8 input circuit and an output circuit controlling the energization of said portion oi said motor means, said output circuit including means for supplying a substantially constant unidirectional voltage thereto, means in said input circuit for supplying a variable controlling voltage thereto to aiiect the current ilow in said output circuit and hence to vary the energization of said portion oi' said motor means, means unaffected by the l0- magnitude of the voltage supplied to said input circuit for periodically interrupting the supply of said unidirectional voltage to said output circuit, and means ior momentarily supplying a an electronic discharge device having an inputcircuit and an output circuit controlling the energization of said portion of said motor means,

said output-circuit including means for supplyingA a substantially constant unidirectional voltage thereto except for periodic intervals, means in said input circuit ior supplying a variable controlling voltage thereto, and means for periodically increasing the magnitude of the voltage applied to said input circuit for relatively brief intervals of' time so as to periodically cause curv rent iiow through Saidbutput circuit when the value of said variable controlling voltage is such that said current iiow would not otherwise take place.

l2. In a motor control system of the follow up type, a motor means, a device positioned thereby,

means for so controlling the energization oi said motor means as to control the extent and direction of movement of said device by said motor means, said last named means comprising an .electronic discharge amplifier having an output circuit controlling the energization' of said motor means and a control element controlling the iiow of current through said output circuit, means for applying a signal voltage to said control element,

said last named means comprising an impedance 50 Vmeans, means for applying an input' voltage to 13. In combination, an electronic discharge l amplifier having an output circuit adapted to control the energization of a load, said amplifier comprising a control element for controlling the discharge thereof, means in said output circuit for applying a. voltage to said output circuit continuously except for periodic intervals of time o! relatively short length to provide a plurality of cycles of output circuit voltage, means for applying a variable control voltage to said control element of said discharge device, and means periodically operative only during certain of said cycles oi said output circuit voltage to increase the magnitude of the voltage applied to said control -element fora relatively brief period of time, the

amplifier conductive so that when said control voltage is relatively small. said ampliner is conductive only during said certain cycles but ia not conductive during the remainder.

14. In combination, an electronic discharge ampliiler having an output circuit adapted to control the energization o! a load. said amplifier comprising a control element for controlling the ilow of current through said output circuit, means in said output for cyclically applying a voltage to said output circuit, means i'or applying a variable control voltage to said control element of said discharge device, and means periodically operative only during certain of said cycles ot said output circuit voltage to increase the magnitude of the voltage applied to said control element for a relatively brief period of time. the magnitude of said increase being insuilicient in the absence of a control voltage to render said amplier conductive so that when said control voltage is relatively small, said amplier is conductive only during said certain cycles but is not conductive during the remainder.

15. In combination, a gas illled electronic discharge device having an output circuit adapted to control the energization of a load, said discharge device comprising a control element for controlling the discharge thereof. means in said output circuit for cyclically applying a voltage to said output circuit, means for applying a variable control voltage to said control element o! said discharge device, and means operative during only certain of the cycles of said output circuit voltageV to successively change the magnitude of the voltage applied to said control element by different amounts during` successive cycles of said output circuit voltage and for ilxed periods of time, the greatest change being insuiilcient in the absence of a ,control voltage to cause discharge of said discharge device. so that when said control voltage is relatively small said discharge device discharges during part or all o! said certain cycles but does not discharge during the remainder.

16. In combination, a gas illed discharge device having an output circuit adapted to control the energization of a load, said discharge device comprising a control element for 'controlling the discharge thereof, said output circuit including means for applying a voltage to said output circuit continuously except for periodic intervals of time of Arelatively short length so as to provide a plurality of cycles of output circuit voltage, .means for applying a variable control voltage to said control element of said discharge device,

and -means operative during only certain of the cycles of said output circuit voltage to successlvely change the magnitude of the voltage applied to said control element by diilerent amounts y during successive cycles of said output circuit voltage and i'or ilxed periods of time, the greatest change being insuillcient in the absence of a control voltage to cause discharge of said discharge device, so that when said control voltage is relatively small said discharge device discharges during part or all of said certain cycles but does not discharge during the remainder.

17. In a motor control system ofthe follow up type. a motor means, a device positioned thereby, a balanceable impedance network comprising a control impedance continuously variable in accordance with variation in the value of a controlling condition and a rebalancing impedance variable in accordance with the position of said motor means, said network having input and out put terminals', means having continuous connections to said input terminals for continuously 'applying a voltage thereto, means for periodically increasing the voltage applied by said last named means for intervals, the duration of which is a small traction of the duration of the intervals of normal voltage, without interrupting said connections to said input terminals, current controlling means for so controlling the energization of said motor means as to control the extent and direction of movement of said device by said motor means, and means responsive to the voltage across the output terminals of said network for controlling the operation of said current controlling means.

HENRY E. HARTIG.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,867,398 Cockrell July 12, 1932 1,904,485 Livingston Apr. 18, 1933 .1,914,481 Brown June 20, 1933A 1,957,016 Loudon May 1, 1934 1,960,350 Shackleton May 29, 1934 1,977,256 Swart Oct. 16, 1934 2,047,984 Riggs June 21, 1936 2,085,100 Knowles et al. June 29, 1937 2,100,460 Specht Nov. 30, 1937 2,161,693 Baier June 6, 1939 2,164,728 n Wey July 4, 1939 2,175,920 Schnarz Oct. 10, 1939 2,175,921 Schnarz -,Oct. 10, 1939 2,242,948 Gulliksen May 20, 1941 2,246,905 Uehling June 24, 1941 Re. 22,123 Edgerton June 23, 1942 OTHER REFERENCES Hot Cathode Thyratrons," General Electric Review, vol. 32, No. 7, July 1929, pages 390-399. 

